The invention relates to an information-bearing construction such as a letter, ticket, etc. wherein indicia must remain undetected for effective utilization thereof by the intended recipient. A lottery ticket may serve as a model for such information-bearing members, but it should be obvious that it represents but one of many applications for such a construction. For example, such articles have substantial utility in the mailing of credit cards, transferral of such military information as code keys, the transferral of confidential business information and the like.
Blush coatings have been used in the construction of lottery tickets, of packages for lottery tickets, and of like items where it is desirable to detect tampering with the article by thermal means. See, for example, U.S. Pat. No. 4,120,445. In the aforesaid patent, it was also proposed to make a blush coating with a dye incorporated therein so that, on exposure of the coating to solvents, the dye would become solubilized, greatly increase its visibility and indicate the fact that the blush coating had been exposed to solvents.
This procedure, whereby dye was added to the blush-coating is found wanting in practice, especially when the blush coat is used in a pouch as defined in U.S. Pat. No. 4,120,445. A problem arises from the fact that, e.g., aliphatic-soluble dyes tend to bleed into a paper substrate and render a "false alarm" with respect to suspected tampering. In some cases the bleeding is slow and is better termed "migration." In such cases the dye migrates into the substrate paper and leaves an ambiguous coloration which may give a false indication of tampering to a customer if not to a more sophisticated inspector. Moreover, the dye tended to be soluble in oils present in the skin and become activated during handling.
As a consequence of these problems, it seemed necessary to remove the dye from the blush coating, at least in the areas of a ticket or pouch were it would tend to cause the aforesaid problems. As a practical matter, it was left that the blush coating was a detection means for thermal-tampering, and a separate dye layer was to be utilized for detection of solvent-tampering. The present inventor determined to find a practical way to combine thermal and solvent detection in a single coating system without encountering the problems described above.